Abstract 2562: Cell populations in human breast cancers are molecularly and biologically distinct with age

Abstract Aging is associated with increased breast cancer risk and outcomes are worse for the oldest and youngest patients, yet it is unknown how cells in the breast tumor microenvironment (TME) are impacted by age or how age contributes to disease pathology. Here, we discover age-associated differences in cell states and interactions in human estrogen receptor-positive (ER+) and triple-negative breast cancers (TNBC) using computational analyses of existing bulk and single-cell gene expression data. We developed the age-specific program enrichment (ASPEN) pipeline, revealing age associations by correlating gene expression and pathway enrichment to age using single cell RNA sequencing (scRNAseq) data. Using the scRNAseq and spatially resolved breast cancer atlas (Wu et al., Nature Genetics, 2021), we identified cell-specific, age-related transcriptional programs in TNBC and ER+ breast cancer. ASPEN revealed increased tumor cell epithelial-mesenchymal transition (EMT), cancer-associated fibroblast (CAF) inflammatory responses, and T cell stress responses with age in TNBC. ER+ breast cancer is dominated by increased luminal cell activity and reduced immune cell metabolism with age. Analysis of differential gene expression between younger and older patients followed by GSEA using the METABRIC bulk gene expression dataset (n = 63 TNBC >65 years, n= 50 TNBC <45 years, n = 386 ER+ >65 years, n = 86 ER+ <45 years) confirmed enrichment of immune pathways (e.g., antigen processing and presentation, immune response) with increased age in TNBC, and pathways related to oncogenic signaling (e.g., TP53 and RB1 targets) and breast biology (e.g., mammary stem cell, luminal v basal) enriched in younger donors in ER+ breast cancer. Cell interactome analysis revealed candidate signaling pathways that could drive these cell states. Expression of the immune-inhibitory protein, Galectin-9 (LGALS9), was observed in both age cohorts in TNBC, yet interactions with the receptor TIM-3 (HAVCR2) were elevated in the younger cohort and those with the receptor prolyl 4-hydroxylase beta (P4HB) were exclusive to the older cohort. Interactions between the EMT-inducing factor, PLAU, expressed by myCAFs and monocyte/macrophages, and its receptor, PLAUR, on cancer cells, were increased with age in TNBC, supporting the finding of increased EMT signatures with age. In ER+ breast cancer, adhesion proteins and extracellular matrix (ECM) engagement comprised most signaling interactions in both age cohorts. Nearly all adhesion/ECM signaling involving either cancer luminal A cells, differentiated perivascular-like cells, or macrophages were enriched in the older cohort; those involving iCAFs, myCAFs, and ACKR1+ endothelial cells were enriched in the younger cohort. This work reveals key biological differences with age at cell type resolution and lays a foundation for discovery of new, age-adapted therapeutic interventions for breast cancer. Citation Format: Adrienne Parsons, Esther Sauras Colon, Milos Spasic, Busem Binboga Kurt, Beyza Koca, Meghana Manjunath, Dimitry Lineker, Ashka Patel, Craig Snow, Alexander Swarbrick, Rachel Freedman, Elizabeth Mittendorf, Peter van Galen, Sandra McAllister. Cell populations in human breast cancers are molecularly and biologically distinct with age [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2562.